The long-term goal of this project is to fully characterize the mechanisms by which neutrophil serine proteases regulate the inflammatory responses. We hope that information gained from these studies can be used to develop strategies to inhibit the activity of these proteases in inflammatory diseases while preserving their ability to kill invading pathogens. Over the past several years, we have learned that, more than being degradative enzymes, neutrophil serine proteases can act as specific regulators of inflammation by modulating the release of cytokines and chemokines as well as activating specific receptors. However, the exact mechanism by which these proteases exert these regulatory effects are still unknown. To further define how neutrophil serine proteases modulate the inflammatory responses, we propose these aims: 1. We will define the mechanisms by which cell-surface-bound cathepsin G (CG) modulates neutrophil effector functions. Our data indicate that extracellular CG cleaves a yet-unidentified molecule and this proteolytic modification enhances neutrophil effector functions. We have identified two candidate proteins as potential binding partners of or substrates for CG, syndecan-4 and S100A9. Here, we will determine whether the proteolytic modification of these candidate proteins by CG will directly affect neutrophil effector functions. 2. We will create a loss-of-function mutation model for proteinase 3 (PR3). to define its role in IL-1P processing and its contribution to inflammation in vivo. Our preliminary data suggest that in a viral-induced upper respiratory tract infection model, proteinase 3 (PR3) plays an important and non-redundant role in the local processing and release of pro-inflammatory cytokine IL-1p. To definitively study the role of PR3 in inflammation in vivo, we propose to generate a loss-of-function mutation in PR3. We will fully characterize the PR3-deficient mice and use these mutant mice for in vitro assays and in vivo models to define the role of PR3 in neutrophil functions and in IL-1(3 processing. 3. We will generate a murine model of anti-neutrophil cvtoplasmic antibody (ANCA)-mediated inflammation and determine the factors that dictate disease development. ANCAs are associated with several smallvessel vasculitides, including Wegener's granulomatosis, microscopic polyangiitis, and Churg Strauss syndrome. In 90% of the cases, ANCAs are directed against myeloperoxidase (MPO) or PR3, although ANCAs specific for other granule serine proteases such as CG and NE are also found. Here, we propose to determine whether ANCAs directed against different neutrophil serine proteases are pathogenic in the murine system. We also hypothesize that decreased expression of complement regulators in the kidney mav be a determinant that influences the severity of tissue damage in the target organ.